Traffic monitoring systems



Jun 27, 6 1.. cAsc-lATo 3,328,791

TRAFFIC MONITORING SYSTEMS Original Filed Jan. 13, 1961 6 Sheets-Sheet l:5Tfil. (ONE OF MANY) I CONTROL EQUIPMENT 4 36 MONITOR U 3 C I L ooo 242;, if i OUTPUT I \TRAFFIC SIGNAL CONTROLLER P l ADAPTER DIGITAL CLOCK 4T E 50 INPUT 4 COUNTER R VEHICLE UNIT DETECTOR I a4 MONITORS OUTPUTUNITS FIG. 2'

COUNTER UNITS COMMON CHASSIS POWER SUPPLY 4d INVENTORS LEONARD CASCIATOBy JOSEF KATES Mrm ATTORNEYS 1.. CASYCIATO June 27, 1967 TRAFFICMONITORING SYSTEMS 6 Sheets-Sheet 2 Original Filed Jan. 13,

INVENTORS LEONARD CASCIATO JOSEF KATES FIG. 3

TO FIGA M ATTORNEYS Original Filed Jan. 13, 1961 6 Sheets-Sheet 4 HOLDACTUATE I 1 VINTERLQCK o T ACTIUATE H g OUTPUT g? I 754 6,] IP 5! FROMCOMPUTER 46k 200 2/4; T 3 2/0 2 ZM\- 220 /77 H Al i 4 77.9 22 Y ,75 0.c.

HOLD RELAY RELAY CONTACTS 200 RELA CONTACTS- 206 5' 1.9.0 OU U OUTPUTDIGIT PULS 2% 32 0 .96 72 m9 I44 7.90 2/6 i5? 218 READ HOLD EAD DIGITPULSES INVENTORS LEONARD CASCIATO FIGS BY JOSEF KATES June 27, v CASCMTO3,328,791

DRAFFIC MONITORING SYSTEMS Original Filed Jan. 13, 1961 6 Sheets-Shec 524; 242 COUNTE P R FIG.7

22$ 7 if ro REMOTE .7 PRESSURE 2:2 swwc TO COMPUTER 266. A v DIGITALTIMING 2M PULSES FIG 9 374 PROGRAM REGISTER 5w DISTRIBUTOR 3M ,AoonsssREGISTER 274 OPERATION REGISTER INVENTORS LEONARD CASCIATO BY JOSEFKATES UPPER LOWER Mam ACCUMULATORS ATTORNEYS June 1967 L. CASCIATOTRAFFIC MONITORING SYSTEMS 6 Sheets-Sheet 6 Original Filed Jan. 13, 1961DIGITAL TIMING PULSES UNITS OUTPUT T0 COMPUTER STORAGE mm mm N E V cA IK 3 D C 3 m 3 NH mm 1 I I I l I I .1 L J 4 A Y a m B E 66 UEE H W OP TUU E OM smR ow HTS s w a 1 8 2 L w w G F W m T M N 2 n k m .C. D D

ATTORNEYS United States Patent 3 Claims. (Cl. 340-324) This is adivision of application Serial No. 82,580 now Patent No. 3,254,324.

The present invention relates to methods'and apparatus for controllingtraific signals.

In large cities, with ever-increasing traific and trafiic congestion,there has been a rapid rise in the number of signal-controlledintersections. In a typical modern city, the concentration of traflicsignal installations varies at different parts of the city, and mayoften exceed a density of 100 per square mile. The traflic patternswhich these signals are intended to control result from an intricaterelationship 'between business, industrial and residential factors. Theconcentration of vehicles varies from a low level at night to a maximumduring rush hour conditions. The morning rush hour trafiic is usuallydrastically dilferent from the evening rush-hour traffic, and trafficpatterns within a given rush hour period may change considerably.Furthermore, acute problems develop when the otherwise normal trafiicpattern for any given time of the day is disturbed locally. This mayresult from routing of emergency vehicles past the rest of the traflicor, in the case of accidents, traflic may be stopped entirely at certainspots of the city.

Considerable progress has been made in the past towards improving thecontrol of traific signals with more versatile control methods andequipment. For example, the isolated fixed-time tratfic signalcontroller has been provided with synchronizing devices sothat a seriesof traffic signals distributed along a thoroughfare may be variouslycoordinated 'for special advantages. The signals may be offset in timeso that traffic moving in one direction may proceed ata predeterminedconstant speed without stopping. In theextreme case, when the timeoffsets are made zero, the signals will change indicationssimultaneously. Further improvements involve a choice of severalfixed-time. settings, the change from one timing schedule to anotherbeing governed usually by some form of time clock.

This fixed-time class of signal equipment is insensitive to trafiicmovements and operates satisfactorily mainly in those situations wheretraflic patterns are uniform and fairly predictable. Greater improvementhas been made in the control of traffic signals by the development ofequipment which does respond in some manner or other to actual trafficmovements. For example, at an individual intersection the signals can beoperated so that the right-of-way time will be divided betweenintersecting streets in proportion to the volumes of traflic movingalong these streets. In the extreme case, right-of-way may remaincontinuously with one street in the absence of traffic on the crossstreet. A network of traific signals may be operated in atrafiic-responsive or trafiic-actuated manner in the following way: agroup of signals may be operated with a short time cycle when trafficvolumes are low and longer time cycles when traffic volumes are high.This has the advantage on the one hand of allowing low-volume trafiic tomove quickly without undue waiting time'for cross street trafiic, and onthe other hand of minimizing the time lost in starting: and stoppingheavy trafiic. In coordinated traffic-actuated systems such as these,pre-set cycle times and olfset adjustments are selected automatically onthe basis of measured traffic volumes rather than by a time clock. Theoperation of any form of traffic-actuated signal equipment depends uponvehicle detectors which may be required on some or all approaches to anindividually controlled intersection or at certain strategic locationswithin a system of controlled intersections.

Such equipment has recently been finding widespread usage throughout anumber of cities of all sizes, and in spite of its relatively high costhas in some cases been installed on a city-wide basis involving theexpenditure of several millions of dollars. The reason for the greatemphasis on improving traific signal systems is that even a smallimprovement in street utilization brought about through the betterregulation of vehicular traflic flow can be worth the equivalent of manymiles of new road facilities while costing only a fraction of the amountrequired for building new or widening existing roads.

However, in spite of the improvements brought about through the use ofthese modern forms of trafiic signal equipment, the increasingcomplexity of traffic movements tends to render even the most up to datetraffic signal controllers less and less effective. In spite of theirmechanical and electronic complexity, existing forms of traffic controlequipment can respond only in a very limited way to changes in trafiic.Equipment which performs best at an individual intersection cannot ingeneral be coordinated into a system of trafiic signals except in a veryloose manner. Equipment which is used for coordinating a system oftraflic signals in general operates according to average trafiicconditions within the system and does not adjust to suit localemergencies. Very frequently automatic traific signal equipmentlabouring within its limitations, will systematically generate trafiictroubles rather than alleviate them. For example, if 'for any reasontraflic congestion should occur in the vicinity of a traific detector,trafiie may become stationary and the counter will receive no furtherindications of the movement of vehicles. This can cause the automaticequipment to resond as if there were no vehicles at all at a time whenthe street may be full of vehicles. Similarly, vehicles may be expeditedinto a trouble area at a time when restraints should be imposed toprevent cong estion from becoming widespread. Even the best of currentlyavailable equipment is not sufficiently flexible to deal with situationssuch as these.

A further drawback to the operation of this traffic signal equipment isthat experience plays no part in its overall operation. No record iskept as to how the system reacted relative to a given traflicconfiguration and there is no Way of evaluating the efiectiveness of thecontrol system other than by direct observation and qualitativeevaluation, The trafiic engineer has at most a daily record of countsfrom certain detectors which he must evaluate manually in makingempirical adjustments to the settings of the automatic equipment. Alarge number (if not all) of the fixed settings must be made at thecontroller box at the intersection. To change, even in a minor way, thechoice of set-- tings available to the automatic equipment involves agreat deal of time and a lot of Work. For example, one widely usedautomatic traflic-actuated controller has over thirty adjustments whichmust be made manually. Additionally, these automatic systems requirecomplicated equipment at the street corners which is not only expensiveand complicated to adjust, but also very costly to maintain.

The present invention describes a tratfic signal control system which isgenerally free of the above limitations. It permits, in a very flexiblemanner, timing of traffic signals to best suit both the requirements ofthe individual intersection and the performance of the traffic signalsystem as a whole. It is capable not only of controlling traflic in avery versatile manner but also of evaluating the quality of the resultsand of using accumulated experience in automatically optimizing itsperformance.

An object of the invention resides broadly in the provision of novelmethods and apparatus for controlling the timing of trafiic signals. Animportant feature of the invention resides in the use of a moderndigital electronic computer for controlling multiple signallizedintersections in a completely automatic traffic-responsive manner Thiselectronic computer, located at a suitable remote control center, isconnected, as by multi-conductor cable, to the trafiic signal equipmentat the various intersections. A modification-unit attached to each ofthe individual trafiic signal controllers permits the computer toremotely take over control of the signals or to release them back tolocal operation.

Traffic detectors, of which a variety of types are available, aresuitably located throughout the network of streets. These detectors arearranged to send traffic counts directly, as by multiple conductorcable, to the computer. In one embodiment, traflic counts only aretransmitted, but additional traflic information such as speed, volumes,density, etc., could advantageously be used. Additionally, indicationsof the signals showing at each intersection are transmitted directly tothe central computer. At the central control location, a special timeclock is connected to the computer to provide exact information on thetime of day and to provide a real time base to allow the computer tocalculate, for example, rates of flow of traffic from the trafliccounts.

Apparatus is provided at the central location for translatingindications from the traific signal equipment and from the trafficdetectors into input signals in suitable form to be utilized by thecomputer, and for translating output signals from the computer intocontrol signals suitable for actuating the traflic signal equipment.

With the above arrangement of equipment, the electronic computer at alltimes has a continuous external supply of information on vehiclemovements, signal indications and time, When automatic control is ineffect, the computer takes over direct control of the signals. The localcontroller timing mechanisms are made inoperative and no change of anyof the signals can occur unless the computer transmits the appropriateelectrical impulse. The timing of each phase of the signals is under thecomplete control of the computer and is independent of any adjustmentsat the local signal controller. If for any reason central control shouldfail, or if the communications link between the computer and the remoteequipment should become inoperative, control of the signals willautomatically revert back to the local signal control mechanism, thusproviding fail-safe standby operation of traffic signals in the event ofsystem malfunction. Trafiic signals can be brought under or releasedfrom central control individually, in groups, or altogether, dependingupon requirements. The central control in the form illustrated belowalso includes provision for manually controlling the signals from theremote control center, but this feature is only rarely used as a testfeature in conjunction with initial installation.

In controlling the traific signals, the computer is guided by what iscalled the Master Control Program which is a set of coded instructionssupplied in program form as by the computer programming personnel andstored electronically within the computer. This Master Control Programis made up of many subsets or subroutiness of instructions, eachsubroutine containing up to several hundred individual instructions.Each subroutine describes a particular maneuver which the computer mustperform. For example, one subroutine instructs the computer how to readin traffic data and where to store it for immediate or future use,Another subroutine instructs the computer how to take over control of atraffic signal. Still another subroutine instructs the computer how todetect traffic congestion, and so on. By means of these subroutines, thecomputer is able to control the traffic signals according to a greatvariety of traffic control concepts, and is able to evalute the resultsthat are produced.

In addition to these subroutines, there are stored within the computertables of data which describe the local conditions at each intersection.For example, the data table for a particular intersection would listsuch information as the number of lanes on each approach, whether or notparking is allowed at any time of day, how far the detectors are locatedback from the cross walks, and so on. When the computer is applying acertain concept of control (control mode) to a traffic signal, itautomatically specializes the general control principles to suit theparticular location.

It is to be noted that the computer is not restricted to following thesame repetitive path of computation in converting information on trafficmovements into timed signal actuations. The computer can not only beprogrammed to carry out computations and follow exceedingly complextrains of logic at very high speed, it can also be programmed to makechanges in the list of instructions it is carrying out. It is this verypowerful feature of the computer which makes it so versatile. Given asuitable starting point for controlling traffic, the computer can beprogrammed to learn from experience and to continuously optimize theeffect that signal actuations are producing on trafiic.

In the illustrative embodiment of the invention, the Master ControlProgram comprises a large number of preselected groups of subroutinescalled Control Plans. Each Control Plan specifies the control subroutine(or control mode) which is to be applied to each intersection. Parametertables for each intersection accompany each Control Plan and serve thepurpose previously described. Each Control Plan corresponds to acompletely different trafiicactuated signal system. The number ofControl Plans which can be stored within the computer is virtuallyunlimited. For example, up to fifty different Control Plans, each ofwhich would be suitable for controlling a network of one thousandtraffic signals, could be stored on a single reel of magnetic tapeassociated with the computer. To add to or make changes in the programsor plans stored within the computer requires no mechanical changes,either at the central control area or at the individual signals.

The change from one control plan to another may be made at the computerconsole or it may be made automatically by the computer. In the lattercase, the computer uses certain computer information on current trafiicbe haviour, coupled perhaps with information based on time of day, andon certain information acquired through experience in dealing with othertraffic situations. For this purpose the Master Control Program includesone or more subroutines which enables the computer to determine which ofthe various control plans is to be put into effect at any given time.One refinement is to have a single completely generalized Control Planwhich the Computer modifies from time to time to suit the changingtraffic picture.

It is accordingly an important object of the present invent-ion to adapttralfic-signal controllers to control by an electronic computer, and itis a further and related object to create an integrated systemcomprising a large number of traflic signals, each having its individuallocal control apparatus, and a centrally located electronic computer.Further objects relate to the methods of controlling the selection ofthe mode of operation of coordinated traflic signals, :as well as thecharacter and control of the timing cycle of any individual traflicsignal, separately, or as part of a larger system.

Among the more specific objects of the invention are the following:

To provide an attachment for a tralfic signal unit by 5. means of whicha central computer can assume control and suppress local control of thetrafiic signals;

To provide a monitoring system for remote indication of the phase ofoperation of each local t-rafiic signal or synchronized group of localtraffic signals;

To translate the transmitted indication of the phase of signal operationof each key local traflic signal into digital data form recognizable bya computer;

To provide a phase monitor of minimum complexity which is nonethelesscapable of providing an indication of many different control conditionsthat prevail, from time to time, at the local trafiic signal, and inthis way to provide practical apparatus that can be utilizedeconomically in a large system;

To provide apparatus for transmitting vehicle counts detected atintersections to a central location and to provide apparatus of minimumcomplexity for supplying vehicle-count information in digital formuseful in the computer, thereby making practical a system that caneconomically utilize large numbers of vehicle detectors and countindicators;

To provide a mode of surveillance of the pattern of traflic signals ineffect at the computer, such that during the individual portions of eachcycle of traflic-signal operation, the computer can make repeatedevaluations of the local conditions and, in individual instances, modifythe duration of the current phase;

To transform the information developed in the computer into signal formeffective to exercise the requisite control over the remote trafficsignal control units;

To establish initially any phase relationship between the trafiicsignals of a coordinated group, as required by the selected plan,whether synchronized or staggered; and

To provide an integrated traflic control system utilizing a centraldigital computer wherein a common source of calendar and time-of-dayinformation is effective to measure time intervals in evaluating trafficdensity, to provide a common time base for the entire coordinatedtnafiic signal control system, and to provide calendar and time-ofdayinformation in a form useful to the digital computer in calling intoeffect any of the stored predetermined plans of traffic signal control.

The nature of the invention and various further objects and features ofnovelty will be apparent from the following detailed description of anillustrative embodiment of the invention in its various aspects.Reference is made in this description to the accompanying drawings whichconstitute part of the disclosure. In the accompanying drawmgs:

FIG. 1 is a diagram illustrating one of a large number of trafiic signalinstallations connected to the central control equipment;

FIG. 2 is a perspective view of a portion of the central controlequipment for coordinating the digital computer at the central locationwith a number of traffic signal installations at various locations ofthe system;

FIG. 3 is a wiring diagram of a local traflic-signal controller formingpart of the local traflic signal installation in FIG. 1;

FIG. 4 is the wiring diagram of the monitor shown in FIG. 1 forproviding information at the central control equipment to indicate thephase in the cycle of operations of a distant trafiic signal controller;

FIG. 5 is the wiring diagram of the output unit in the central controlequipment, shown in FIG. 1, for enabling the computer to control andactuate the controller of a local traffic signal unit remote from thecomputer;

FIG. 6 is the timing diagram of certain portions of the apparatus inFIGS. 4, 5 and 7;

FIG. 7 is the wiring diagram of the stepping-switch continuous counter,shown in FIG. 1, for relaying vehicle-counts from the remote vehicledetector to the digital computer shown in FIG. 1;

FIG. 8 is the wiring diagram of a portion of a digital clock that formspart of the central control equipment of FIG. 1; and

FIG. 9 is a block diagram of a digital computer forming part of thecentral control equipment.

Referring now to the drawings, FIG. 1 represents, diagrammatically, anelemental portion of an integrated traffic control system, the apparatusin FIG. 1 including central control equipment 10, a single remote orlocal tralfic signal unit 12, and a single vehicle detector 14associated with trafiic along one of the routes controlled by signalunit 12. Units 12 and 14 have wired connections to the central controlequipment, represented by single lines in FIG. 1. The connections hereprovided (FIGS. 3, 4, 5 and 7) are pairs of wires such as are used intelephone circuits, but it will be appreciated that other communicationslinks may be substituted for providing the necessary interconnectionbetween the central and the remote or local equipments.

As shown, three pairs of wires 16A, 16B and are represented in FIG. 1 bythree single lines, these three pairs of wires extending between trafficsignal controller 18 at the local installation and monitor 20 of thecentral control equipment. This monitor provides an indication at thecentral location in both visual form and in a form that can be utilizedin a digital computer, representing the phase of the traflic signalcontrol cycle at the local installation.

At the local traffic signal installation, there is an adapter 22 whichis added to the traflic signal controller that enables the centralcontrol equipment 10 to seize control of and to actuate the localtrafiic-signal controller 18. Adapter 22 is connected by two pairs ofwires 24 and 26 to an output unit 28 in the central control equipment10.

The single vehicle detector 14 that forms part of the local traffi-csignal installation illustrated in FIG. 1 is connected by a pair ofwires 30 to an input counter unit 32 in the central control equipment.It will be appreciated that each local trafiic signal installation willinclude a number of vehicle detectors 14, suitably located to indicatethe flow of trafiic. Thus, there may be two trafiic detectors 14 in anorth-south street at opposite sides of the intersection and in oppositelanes, northbound and southbound, respectively; and there may be twosimilarly lo cated vehicle detectors 14 in the cross-trafiic route forproviding an eastbound traffic count and a westbound traffic count. Moreelaborate installations may involve multiple counters along each route,including a first vehicle detector at a point of approach to asignalized intersection for counting vehicles approaching theintersection, and another detector in the same route close to theintersection in order to provide information as to number of detectedapproaching vehicles that may be assumed to have actually entered theintersection, the difference in these counts representing the number ofvehicles waiting. Each time a vehicle passes detector 14, an impulse istransmitted along line 30 to the input counter unit 32 at the centralcontrol equipment 10. If detector 14 is in the form of a simplewheel-actuated pressure switch, the number of two-axle vehicles can bederived by a scale-oftwo counter (not shown) that provides one impulsein response to each pair of switch actuations, or this conversion can beprogrammed in the computer.

Each local trafiic signal installation 12 includes its own trafiiccontroller 18 and its own adapter 22, complemented by an appropriatenumber of vehicle detectors 14; and these units transmit information tothe central control equipment 10 and receive control impulses from thecentral control equipment. In the complete system there are as manymonitors 20 and output units 28 as there are separately controlledtraffic signal installations or synchronized groups of trafficinstallations in the system. Similarly, there are as many input counterunits 32 in the complete system as there are vehicle detectors 14 in thesystem.

A digital clock 36 forms part of the central control equipment, andprovides numerical input in a form useable by the computer, being in theform of the number of seconds elapsed since some arbitrarily chosenstarting time, e.g. noon or midnight.

All of the monitors 20, the output units 28, the input counter units 32,and the digital clock 36 have appropriate connections to the digitalcomputer 34. The internal wiring and operation of the local trafficsignal controller 18 and adapter 22 which are shown diagrammatically inFIG. 1, are discussed in detail below in connection with FIG. 3.Similarly, monitor 20, output unit 28, input counter unit 32 and digitalclock 36 of FIG. 1 have circuits shown in FIGS. 4, 5, 7 and 8,respectively, and are discussed in detail below. A block diagram ofcomputer 34 appears in FIG. 9 and is similarly discussed in some detailbelow.

The central control installation, in addition to the computer anddigital clock, involves as many monitors 20, output units 28, inputcounter units 32 as are required by the number of differently controlledremote traffic-signal installations. The monitors, output units andcounter units may be physically assembled in the manner indicated inFIG. 2. Six monitor units 20 are illustrated, as are the correspondingsix output units 28 for six remote trafficsignal installations. A largemember of counter units 32 are shown in the same installation. A commonchassis 38 is provided for containing the circuit equipment used incommon by all of the monitors, the output units and the counter units;and a common power supply 40 is included for the foregoing equipment.

T raflic signal controller and remote indicating and control adapter Theinternal wiring of traffic signal controller 18 and the adapter 22,forming part of the local traffic signal unit 12 in FIG. 1, is shown inFIG. 3. The traific-signal controller includes a continuously runningA-C synchronous dial motor 42 having an electromagnet 44 and a combinedarmature and brake 44a, and three dial cams 46, 48 and 50. In practicethe cams are constituted of a single axially grooved cylinder in whichso-called keys 51 are inserted. The keys 51 have radial projections andact as cams that cooperate, respectively, with normally openc-am-actuated switches or contacts 52, 54 and 56. The projections of theinserted keys are located at different axial positions on theirsupporting cylinder, so that each key cooperates with its correspondingswitch. A number of keys cooperate with switch 52, while only one key isprovided for actuating switches 54 and 56.

A drum-advance solenoid 58 is provided for operating a drum by means ofa ratchet-and-pawl indexing mechanism. This indexing mechanism includesarmature 73, pawl 74, and a spring 76 that normally holds the pawl 74 inthe position illustrated. Pawl 74 cooperates with a ratchet 78 that issecured to a common drum shaft. When solenoid 58 is energized, ittensions spring 76 and withdraws the pawl 74 into position for engagingthe next tooth of ratchet 78. Upon deenergization of solenoid 58,tensioned spring 76 advances the ratchet one step.

The drum that is operated by ratchet 78 consists of a series of drumearns 80, 82 and 84 having a plurality of distinctive signal-changingpositions. Cam 80 operates norm-ally closed drum-lock contacts 62. Aseries of earns 82 are provided (only three being shown) for actuatingcontact pairs 83 that constitute a sequencing switch for the trafficlights 85 or other traffic signals at the local traffic intersection.Three cams 84 are used for actuating respective switches for providing aremote representation of the drum position or phase.

The operation of the apparatus thus far described may be brieflyreviewed. Each time one of the keys 51 closes drum-advance contacts 52,solenoid 58 is usually energized. An energizing circuit for solenoid 58may be traced as follows: from A-C supply line 60 through normallyclosed drum-lock contacts 62, through solenoidactuating drum-advancecontacts 52, wire 64, selector switch 66 in its automatic-advanceposition, through lead 68, the normally closed pair of relay contacts90A and lead 70, through solenoid 58, to the opposite alternatingcurrent supply line 72. When the dial motor 42 carries key 51 beyondswitch or drum-advance contacts 52, and allow-s the switch 52 to open,solenoid 58 is deenergized. Spring 76 then drives pawl 74 and indexesratchet 78, and the drum with its various earns 80, 82, 84 advances onestep.

It is possible for the dial, represented by the dial earns 46, 48 and50, to get out of step with the drum cams 80, 82 and 84. In order toassure and to restore the proper relationship between the dial and thedrum, normally closed drum-lock contacts 62 are included in series withdrum-advance contacts 52. When the drum has been indexed to the positionwhere contacts 62 are opened by cam 80, subsequent closure ofdrum-advance contacts 52 will have no eflFect. The dial will continue torotate and switch 52 will close, but the pulse transmitting circuit tothe solenoid 58 is broken. When the dial cams 46, 48 and 50 come intoproper relationship with the drum, dial cam 48 closes drum-releasecontacts 54. These contacts provide a circuit that bypasses drum-lockcontacts 62, thereby energizing solenoid 58, and indexing the drum so asto advance cam and to allow drum-lock contact 6-2 to close once again.The drum and the dial resume operation, properly synchronized. In anormal, synchronized cycle of operation, drum-lock contacts 62 open atthe same time that drum-release contacts 54 close. In normal operation,the drum-lock contacts 62 do not cause a halt in the drum-advancesequence.

Selector switch 66 is illustrated as having an automatic position and amanual position. The automatic position has just been described. Whenselector switch 66 is shifted to the manual position, the circuit fromthe various dialactuated switches or cont-acts is broken and, instead,solenoid 58 is in a circuit that may be energized by operating manualswitch 86. The dial continues to rotate without affecting the drum.Selector switch 66 and pushbutton switch 86 are normally operated by apoliceman under special circumstances.

At the end of an interval of manual operation, the dial and the drum mayvery well be out of sy-nohronism. When switch 66 is returned to itsautomatic position, restoration of the dial cams and the drum intoproper synch-ronism is elfected automatically, as described.

Cams 84 form part of the drum advanced by the ratchet-and-pawl mechanism73, 74, 78. These cams operate respective switches 88A, 88B and 88C.Switches 88A, 88B and 88C are normally open, and they close when thespring-biased contact arm of each switch finds a cut-out in its relatedcam. Cams 84 have portions broken away so that unique combinations areprovided for representing the different drum positions. In thisillustrative embodiment, there are eight different possible combinationsof closed conditions of these switches, so that eight differentconditions of the traffic-signal sequencing switch can be represented bythe combinational condition of switches 88A, 88B and 88C. These switchesare connected by pairs of wires 16A, 16B and 16C to a correspondingremote monitor 20 at the central control equipment 10.

By means of the apparatus in adapter unit 22, the drum-advance solenoid58 can be removed from control by both the solenoid-advance contacts 52and the manual switch 86. This apparatus includes a hold solenoid orrelay 90 having a single-pole double-throw set of contacts 90A and anormally open pair of contacts 90B. The moving arm of contacts 90A isconnected to drum-advance solenoid 58. In the position illustrated(relay coil 90 not energized), contacts 90A connect wires 68 and 70 sothat the circuit from solenoid 58 to auto-manual se- 75 lector switch 66is unbroken. It is possible to energize hold relay 90 from the centralcontrol equipment, by means including wires 24. When this is done,single-pole double-throw contacts 90A reverse their condition and thecircuit from drum-advance solenoid 58 to selective switch 66 is broken.At the same time, contacts 90B are closed, producing two efiects. First,a neon indicator lamp 92 is energized via wires 94 and 96, showing thatthe traflicsignal sequencing switch is under remote control. Second, acircuit is completed from the alternating current supply wire 94 throughcontact 90B and wire 98 to cam contacts 56 and (when the latter close)to brake electromagnet 44. Synchronous dial motor 42 continues to drivecam 50 until contacts 56 close. When this occurs, brake solenoid 44 isenergized and the dial motor 42 is arrested in its position wherecontacts 56 are held closed by the key on dial cam 50. The dialtherefore remains in the fixed position determined by the key on cam 50so long as drum-advance solenoid 58 remains under remote control. Othertraffic signals in the area having previously coordinated operatingcycles and equipped with remote-control adapters may be similarly placedunder remote control. All of those coordinated but individually timedtraific signals are arrested under remote control and they are heldagainst operation by their respective brakes during the period of remotecontrol. When remote control of one or more traffic signals isdiscontinued, they are restored to local control; and when this occursthe respective brakes release the timing dials and the controllers ofeach of the traffic signals of this group will resume operation in thesame relationship that previously prevailed, provided the drums are inthis relationship at dropout, which can be accomplished by the computerprogram.

It has been shown that energization of hold relay 90 establishes controlover drum-advance relay 58 from the remote point. Actuation of thisdrum-advance relay is also accomplished from the remote point, aspreviously indicated, by energizing wires 26. These wires are connectedto remote-control actuating relay 100, and when this is energized, relaycontacts 100A close. This completes a circuit from alternating currentsupply line 72 through drum-advance relay 58, wire 70, through thenormally open pair of relay contacts 90A which are now closed, wire 102,relay contacts 100A, and alternating current supply line 94.

The foregoing description of the local trafiic signal controller 18indicates three changes made at the controller in order to establishremote indication and remote control of the operation. One changeinvolves the utilization of a series of spare cams and cam contacts 84and 88 for remote indication, such cams being commonly available; andanother change involves interposing a pair of relay contacts 90A betweenwires 68 and 70 which were previously an unbroken lead in thelocal-control apparatus. A third change is the connection of the brakecircuit as described and illustrated. Operation of the traific signalcontroller is completely normal when hold relay 90 is not energized.When hold relay 90 is energized, the drumadvance relay or electromagnet58 is placed under control of the remote-control actuating relay 100.After central control is no longer desired, the hold relay 90 isdeenergized and drum-advance relay 58 is restored to its previouscontrol by the motor-operated dial cams 46 and 48. The dial is locked bybrake 44 during remote operation; and when local operation is restored,the dial resumes its advance immediately, in synchronism with all othertraflic signal controllers that were placed under remote control andrestored to local control, provided the drums are in synchronism atdropout.

Monitor 20 In FIG. 3, contact 88A, 88B and 88C, which are operated bythe cams 84, have leads 16A, B and C (FIG. 1) to a monitor 20 of thecentral control equipment 10. The details of monitor 20 are shown inFIG. 4. The main purpose of this apparatus is to provide information forthe computer to recognize the position of the local tratficsignal camsand sequencing switches 82, 83 (FIG. 3) and to provide a displayrepresentation at the central control equipment 10 corresponding to thetraflic signals monitored.

In FIG. 4, a pairs of lines 16A, 16B and 160 are shown connected torespective relays 104A, 104B and 104C. These relays are energized bydirect current from terminals and 112 through normally closed contacts106 of relay 108. For example, a circuit may be traced from the negativedirect-current supply terminal 110 through contacts 106, along commonnegative line 114, along one of a pair of wires 16A, to cam contact 88A(FIG. 3), returning along the other wire of the pair 16A, throughisolating diode 118A, to energize relay 104A, the other terminal of thisrelay extending to the positive direct-current supply terminal 112.

Relay 104A has two groups of contacts, including a set of single-poledouble-throw contacts 120, and four more sets of double-throw contacts120, and four more sets of double-throw contacts 122a, 122b, 1220 and122d. Similarly, relay 104B has two groups of contacts, including agroup having two sets of double-throw contacts 124a and 124b, andanother group having two sets of doublethrow contacts 126a and 12612.Relay 104C has one group of four double-throw contacts 128a, 128b, 1280and 128d, and another set of double-throw contacts 130.

Relay contacts are connected in cascade with contact group 124a and124b, and contact group 128a, 1285, 1280 and 128d, so that terminal 134at one end of the cascade of the contacts is connected through thevarious double-throw contacts mentioned to one and only one of eightoutput terminals 132, depending upon the particular combination ofrelays 104A, 104B and 104C, that are energized at the time. Terminals132 have respective leads designated 1, 2 8 in FIG. 4, thesedesignations representing the eight sequential positions of thesignal-sequencing switch 82, 83 in FIG. 3. The leads extending fromterminals 132 are connected to corresponding contacts of a motor-drivenrotary switch 136, whose moving contact arm 136a extends to a directcurrent supply.

Rotary switch 136 is a normal part of the card-reading apparatus in astandard computer, and this switch produces timed read digit pulses. Thetiming of such pulses in the computer is illustrated in the lower halfof FIG. 6. A pulse will be delivered at terminal 134, which is connectedto the computer storage entry portion of the computer of FIG. 1 at atime in the read cycle which corresponds to the circuit from terminal134 to the particular terminal 132 that is completed by contacts 120,

124a and b, and 128a, b, c and d. In this way, relays 104A, 104B and104C, which are connected to lines16A, 16B and 16C and cam contacts 88A,88B, 88C (FIG. 3), provide read-in information in a form that is useableby the computer. For example, the eight significant positions of thesignal-sequencing switch 82, 83 in the local trafiicsignal unit can betranslated into corresponding timed pulses supplied to the computer in aread cycle, to represent the following local traflic signal phases:

Monitor Relays Number Interpretation Southbound advance green.Northbound advance green. North-South green. North-South green-amber.Westbound advance green. Eastbound advance green. East-West green.

East-West green-amber.

OMMNNooo OOQNNNMO ooMMooMN OOQOaUnPCDNr- There are some conditions whenthe traflic signal for both the North-bound and the South-bounddirections are green. At such times both East-bound and West-boundcommonly have red signals. There is another condition when both East andWest have green signals, the North- South signals are red. Additionally,the North and South can both be amber (or amber and green) while theEast and West are red; and conversely, the East and West can both beamber (or green and amber) while the North and South are red. Finally,there are four conditions when the green light is allowed in only onedirection at any one time, that is, South-bound, North-bound, West-boundor East-bound. These are the signal combinations in the tabulationabove. Other signals and signal combinations may of course besubstituted, and any number of positions may be accommodated by circuitadaptation if the 8-position arrangement is not suitable.

An additional function of the monitor is to provide a visual indicationat the central control location which represents the phase of the localtraffic signals at remote installations. For this purpose, relays 104A,104B and 104C are equipped with the groups of double-throw contacts122a, b, c and d, 126a and b, and 130, connected in cascade, aspreviously described. These contacts are arranged to energize one of themonitor display relays 138a, 138b, 138a 13811. Only one of these relays138 will be energized by the cascaded contacts, as determined by theparticular combination of relays 104A, 104B, 104C that are energized.Relays 138 are energized by alternating current from terminals 140.

It would be feasible to arrange circuits energized by each energizedrelay 138 to represent the North, South, East and West green, amber andred lights, but to do so would involve relatively complex displayapparatus in the central control equipment. Such display apparatus isduplicated for each of the local traffic signal controllers in thesystem, and so simplication of the display is of importance. Theillustrative embodiment shown in the drawing provides the displayinformation without requiring as many indicator lights as there areseparately controlled lights at the traffic controller site.

The display control circuit in FIG. 4 includes a first series ofnormally open relay contacts 142a, 142b 142k and a second set ofnormally open relay contacts 144a, 1441) 144k, selectively operable bythe particular relays 138 having corresponding alphabetic characters.Additionally, a normally open pair of contacts 146a is arranged to beoperated by relay 1382 and a pair of relay contacts 14621 is operable byrelay 138/1. All of the contacts 144 and 146 extend to an alternatingcurrent supply line 150, as do contacts 142a, 142b, 1420, and 142d.Contacts 142e, 142 142g and 14211 extend to alternating current supplyline 150 by way of continuously operating flasher contacts 148. Theother alternating current supply line 152 extends to a series ofNorth-South indicator lamps 154R, 154Y, 154G, and to East-West indicatorlamps 156R, 156Y, and 156G. A set of terminals 160 is provided,connected to the respective lamps 154- and 156, for auxiliary display orfor test purposes.

With the set of contacts 130, 126 and 122 operated in variouscombinations depending upon the energized com bination of relays 104A,104B and 104C, various conditions will be displayed by lamps 154 and156. Thus, for position number 3 in the table, the local traflic signalsfor both North and South are green, and the local signals for East andWest are red. Only relay 104B is energized, so that only relay 1380 willbe selected. This will be represented by a single green light 154G and asingle red light 156R being turned on in the display unit 158. Foradvance to condition #4, relays 104A and 104B are energized, monitorrelay 138d is selected, and contacts 142d and 144d are closed. As aresult the East-West red lamp 156R remains on, while the North-Southgreen lamp 1546, which was on, is turned off and North-South yellow lamp154Y is turned on.

For the purpose of representing Advance Green for one direction whilered is set for the opposite direction at the local controller, thecircuit including flasher 148 is used. There are four such conditions,where only North, only South, only East or only West has an AdvanceGreen indication, represented in the above table by 1, 2, 5 and 6. Wemay consider that condition #1 in the tabulation is in effect at thelocal traflic signal installation, and only relay 104C is energized.Under these conditions, monitor display relay 138a is energized, closingcontacts 142e, 144e and 146a. The red light 156R for East-West isenergized through contact 146a and the red light 154R for North-South isenergized through contacts 144e; and the green light 154G is energizedthrough contacts 142e and through flasher contacts 148. The North-Southlights include a steady red light and a flashing green light, and thisdisplay in the monitor signifies a green light at the local traificcontroller for the southbound traflic only. By like token, when relays104B and 104C are energized, East- West red lamp 156R is on steadily andNorth-South green lamp 154G is energized through the flasher, but theNorth-South red lamp 154R is oflY. The flashing North- South green lamp1546 at the monitor, with lamp 154R turned otf, signifies North-boundgreen only at the local traflic controller. Similarly, in position #6,relays 104A and 104C are energized with the result that relay 138 isselected, and North-South red lamp 154R is steadily on and East-Westgreen lamp 156G flashes, signifying East-bound advance only at the localtraflic signal installation. West-bound advance only is represented bysteady illumination of North-South red lamp 154R and East-West red lamp156R and flashing East- West green lamp 1566. This condition prevails atthe monitor when all three of relays 104A, 104B and 104C are energized.

The foregoing display apparatus in the monitor uses six lamps torepresent twice as many lamps that would otherwise be needed toduplicate the lights at the local traflic signal controller, consideringred, green and amber in each of four directions that may be used invarious combinations. This represents a substantial saving, which isparticularly important because a separate monitor with the necessarycomplement of lights is provided at the central control equipment foreach of the local traflic signal installations in the system.

An appreciable interval of time 0/5 second) elapses during a read cycleof operation of the switch 136. It is desirable that any particularcombination of energized relays 104A, 104B and 104C should not changeduring this read cycle. Otherwise the computer might receive ambiguousinformation. For this purpose a circuit is provided that disconnectsrelays 104A, 104B and 104C from lines 16A, 16B and 16C during the readtime interval. This circuit additionally holds the relays in theircondition prevailing just before disconnection occurred. This circuitincludes relay 108 and a read-hold timing switch or cam contact 162through which relay 108 is connected to the D-C supply terminals and112. The closing of contacts 162 is represented by the read-hold part ofthe timing diagram in FIG. 6. Relay 108 is thus energized for a periodsomewhat longer than that required for the digit pulse generator contactarm 136a to complete its sweep past all of the contents of switch 136.During this read-hold time, relay 108 causes contact 163 to be connectedto D-C supply terminal 110.

Each of the relays 104A, 104B and 1040 has a corresponding holdingcontact 164A, 164B and 164C, and an isolating diode 166 connected inseries with each hold contact. During a read interval, a circuit may betraced from terminal 110 through relay contacts 163, through any one ormore of the holding contacts 164A, 164B and 164C that were closed beforeclosing of contacts 163, and through the corresponding relays 104A, 104Band/or 104C to DC terminal 112. Any relay that was energized beforecontacts 106 are opened remains energized when contact 163 is connectedto DC supply terminal 110, and for this purpose these relays 104A, 104Band 104C have a suitably retarded opening characteristic.Correspondingly, the connection of lines 16A, 16B and 16C to the supplyterminal 110 is broken when contact 106 is opened. As soon as the readinterval is over, contact 163 opens and contact 106 recloses, therebyrestoring lines 16A, B and C, and the remote cam switches 88A, B and Cinto their control relation with respect to relays 104A, B and C.

The apparatus in FIG. 4 converts the information represented by thecombinations of closed switches at the local traffic signals into timedpulses, and thus provides the computer with input information in usefulform, indicating to the computer the phase of the trafiic-signalsequence that prevails at any given time. This is par ticularly usefulwhen the computer initially assumes control of the local trafiic signalcontroller. The phases of the computer signal-controlcycle and of thelocal traffic signal control cycle should initially be brought intoagreement and this agreement should be verified repeatedly. Theapparatus of FIG. 5 utilizes the output from the computer in causingoperation of the local trailic signal controllers, acting throughadapter units 22 in each of the local trafiic signal controllers (FIG.3). The function of the isolating diodes 118 and 166 is to eliminatefeedback paths that would produce undesired cross-coupling betweencircuits.

- Output unit 28 The circuit of the output unit 28 is shown in FIG. 5.This includes three principal relays, an actuate relay 170, a hold relay172, and an interloc relay 174. When hold relay 172 is energized, acircuit is completed that extends from the positive direct-circuitsupply line 175, through normally closed switch contacts 186a and relaycontacts 180, to the pair of lines 24 which extend to hold relay 90(FIG. 3), and thence to the negative return line 177 of the directcurrent supply. Toggle switch 186 is interposed in this line formanually interrupting the hold circuit at the central control equipment.When actuate" relay 170 is energized, another control circuit extendsfrom line 175 through switch contacts 186a and contacts 176 of theactuate relay, to actuate control line 26 for energizing actuate relay100 in FIG. 3, thence to the negative return line 177 of the directcurrent supply.

Supplementing contacts 176 and 180 for energizing hold line 24 andactuate line 26 are a pair of additional push-button switches 1'88 and190. Push-button switch 188 includes two sets of normally open contacts188a and 188k. Contacts 188a, when closed, provide a circuit bypassingrelay contacts 180 ,and switch contacts 186a and thus energize the holdrelay 90 (FIG. 3) when the push-button 188 is manually operated at thecentral control equipment. Similarly, if both push-buttons 188 and 190are operated at the central control equipment, then a bridging circuitextends not only through contacts 188a to the hold line 24, but alsoanother bridging circuit extends from D-C supply line 175 throughcontacts 190 and 188b to actuate line 26.

Operation of a local traflic controller under control of push-buttons188 and 190 at the central control station is only rarely undertaken,being primarily for test purposes.

Relays 170, 172 and 174 are operated by signals from the punch orread-out line 192 from the output of the computer, this output beingapplied to these relays through isolating diodes 194, 196 and 198. Thisoutput appears in the form of pulses which may occur at any one oftwelve parts of an operating cycle, as indicated by the dashes along theoutput digit pulses line in FIG. 6.

Rotary switches 204 and 210, which are actually the same switch and arepart of the computers standard output equipment, operate relay 202,thereby closing relay contacts 200 and operate relay 208, therebyclosing relay contacts 206 at times of the output cycle shown in the 14chart in FIG. 6. Rotary switch 226, which is also part of the computersstandard output equipment, operates relay 224, thereby closing relaycontacts 222 138 shown in the line output hold of the timing chart inFIG, 6. Only certain combinations of the 12 available output pulses areactually used. The actuate relay may be operated by either a 12 pulse, a3 pulse or an 8 pulse as shown in the line actuate relay of the timingchart in FIG. 6, through a circuit consisting of line 192, switchcontacts 186b, isolating diode 194, relay 170, relay contacts 200, andline 177 to the negative side of the DC supply. The timing of relaycontacts 200 will prevent any other impulses from operating actuaterelay 170. While 12, 3 and 8 impulses will always operate actuate relay170 and consequently relay (FIG. 3), they will only be effective inoperating the traffic signals when hold relay 172, and consequently holdrelay 90 (FIG. 3), are operated, as can be seen from FIG. 3. The holdrelay 172 is normally picked up by either a zero or a five impulsethrough a circuit consisting of line 192, switch contacts 186b,isolating diode 196, relay 172, line 214, isolating diode 199, relaycontacts 206, master dropout control 218, and line 177 to the negativeside of the direct current supply.

Once picked up, the hold relay is self-holding through a circuit runningfrom the positive side of the DC supply through line 175, switchcontacts 186a, dropping resistor 212, relay contacts 178, relay 172,line 214, isolating diode 199, relay contacts 206, master dropoutcontrol 218, and line 177 to the negative side of the D0. supply,

Once energized, the hold relay 172 will be deenergized only by theopening of relay contacts 206, which occurs regularly at a late stage ofthe output cycle, as shown in the timing chart of FIG. 6.

However, a bridging path is provided, to bypass relay contacts 206, thispath consisting of line 216 and interlock relay contacts 184. This pathwill be effective whenever the interlock relay is operated, and willprevent the hold relay 172 from being de-energized.

The interlock relay 174 is normally picked up by either a 12, 0, 3 or 5impulse through a circuit running through line 192, switch contacts186b, isolating diode 198, relay 174, isolating diode 199, relaycontacts 206, master dropout control 218, and line 177 to the negativeside of the DC. supply.

Once picked up, the interlock relay 174 remains operated through theremainder of the cycle in which it was picked up through a circuitrunning from the positive side of the supply through line 175, line 179,relay contacts 222, dropping resistor 220, relay contacts 182, relay174, line 214, line 216, interlock relay contacts 184, master dropoutcontrol 218, and line 177 to the negative side of the DC supply. Itreleases near the end of the output cycle through the opening of relaycontacts 222 as previously described.

On most output cycles, it is desired to keep the hold relay energizedwithout causing any actuation. This is accomplished by outputting .a 5impulse which operates the interlock relay 174 and thus prevents thehold relay 172 from being dropped out on that cycle.

A 12, a zero or a 3 impulse will also prevent the hold relay 172 fromdropping out on the cycle in which it occurs, but these impulses willproduce actuations as well. (The computer output is so wired that a zeroimpulse is always followed by a 3 impulse).

Several combinations of output impulses are used to obtain the desiredresults at the controller. The absence of an impulse during any cyclewill cause the hold relay 172 to drop out, if it is energized. A 5impulse will pick up the hold relay 172 if it is not energized and willcause it to remain held if it is already energized. A zero and a 3impulse combination will pick up or hold the hold relay 172 and produce,a single actuation. A zero, 3 and 8 impulse combination will pickup orhold the hold relay 172 and produce two actuations in quick succession.A 12, 3,

15 and 8 impulse combination may be used only if the hold relay 172 isalready picked up, and will produce three actuations in succession.

It will be appreciated that the stepwise advance of the drum cams 80,82, 84 in the sequencing switch contained in unit 18 in some cases willnot effect a phase change, by reason of the number of teeth in theratchet 78 being greater than the number of distinct phases provided inthe sequencing switch by the rise and dwell portions of the respectivecams 80, 82, 84. In such situation, for some actuations of the pawl 74,the stepwise advance of the ratchet 78 may not be sufiicient to changethe condition of the sequencing switch. Therefore, in order to changefrom one phase to the next, it may be necessary in some cases to providemore than one actuating pulse from the central control equipment to thedrum solenoid 58. The provision of plural actuating pulses as describedabove is one way of eifecting desired phase change in this illustrativesituation.

Relays 202, 224 and 208 as well as the master drop out control 218 arecommon to all the out-put units. The hold circuits for all the outputunits pass through the master drop out control. If the master drop outcontrol receives no read hold pulse during a pre-determined period oftime (say 10 seconds) then it will disconnect all the output units andthus release all the controllers to local control. This is a fail-safefeature in case the computer stops for any reason. The master drop outcontrol 218 may, for example, be a thyratron operated relay which opensthe circuit after the prescribed time period.

The hold and the actuate relays can be operated as described above inresponse to properly timed pulses from the computer. Thus a pulse willcause pick-up and holding of the relays 172 and 174, and of the holdrelay 90 at the local traflic signal controller (FIG. 3). Pulses at the0 and 3 times in the cycle will cause pick-up and a single momentaryactuation of relay 170, and of the actuate relay 100 at thecorresponding local traffic signal controller. Pulses at 0, 3 and 8times in the cycle will cause pick-up of the hold relay 90 and twoactuations of the actuate relay 100. Pulses at the 12, 3 and 8 times inthe cycle will cause three actuations of the relay 100 in the localtraffic signal controller, provided the hold relay is in the energizedstate. The master drop-out control 218 is arranged so as to de-energizethe interlock and hold relays 174 and 172 in the event that no pulsesare detected during a preset period, thus indicating malfunction orstoppage of the computer.

From the foregoing description of the output control, it appears that inthe absence of signals from the computer, the remote local trafficcontrollers will operate according to their individual or interconnectedcycles; or, in the event that the computer at the central controlstation indicates that control is to be assumed, the central controlequipment can take over control of the local traffic signal controllers.When this is to be done, the computer compares the numericalrepresentation of the position of the cam contacts 88A, 88B and 88C inthe local traflic signal controller as provided by the monitor (FIG. 4)and the number supplied by the computer to represent the phase in itssignal-control sequence and waits until the desired phase comes intoeifect before assuming control. This is effected by suitable programmingof the computer.

Vehicle counters In connection with FIG. 1, vehicle detector 14 wasdescribed with its wired connection 30 extending to a counter unit 32,there being a sizeable number of vehicle detectors 14 and counter units32 in the system. The internal details of an illustrative input counterunit contained in the central control equipment is illustrated in FIG.7. Line 30 extends to a vehicle detector, being in its simplest form apressure switch 14 actuated by a vehicle. Pressure switch 14 (FIG. 1)completes a circuit from the positive lead 230 of the DC supply (FIG. 7)through relay 232, and via leads 30 and detector 14, to the negativereturn lead 234 of the direct current supply. Momentary energization ofrelay 232 causes closing of its holding contacts 236, these contactsbeing in a circuit which bypasses the line 30 and the remote pressureswitch 14. The holding circuit extends from the negative terminal ofrelay 232, through holding contacts 236, through lead 238 and through apair of contacts 240 (to be described), and thence to the negativeterminal of the D-C supply.

Energization of relay 232 additionally causes closing of its operatingcontacts 242. These contacts complete a circuit from the alternatingcurrent supply terminal 244, through the contacts 242, through counter246, to the opposite terminal 248 of the alternating-current supply.Counter 246 is an ordinary odometer-wheel counter actuated by anelectromagnet of conventional construction, useful for maintaining arunning total of vehicles passing each detector at the central controlequipment. Closing of contacts 242 also applies alternating current to aneon indicator lamp 250 with its series-resistor 252. Contacts 242additionally apply alternating current across the input terminals ofbridge rectifier 254. The direct current output terminals of this bridgerectifier energize electromagnet 256 of a stepping switch. This steppingswitch includes ten contacts 258 which occupy a sector of onethird of arevolution of the wiping contacts 260, there being three such wipingcontact arms 260 so that one of the arms is always in contact with oneof the contacts 258. A full forward stroke of the electromagnet shifts apawl and tensions a pawl-return spring (see parts 73, 74, 76, 78 in FIG.3), and when the electromagnet is deenergized, the pawl operates aratchet to advance the three contact arms 260 as a unit through aone-step range. In this way, one of the wiping contact arms 260 advancesfrom one of the stationary contacts 258 to the next one each time theelectromagnet is energized and deenergized.

Electromagnet 256 of the stepping switch is suitably arranged to opennormally closed contacts 240 when the indexing mechanism approaches theend of its indexing stroke. As soon as this occurs, the holding circuitfor relay 232 is broken. The relay is then deenergized, unless thevehicle that initially actuated the remote pressure switch 14 is stillon the pressure switch. In that event, relay 232 would remain energizedand, correspondingly electromagnet 256 would remain energized until thevehicle releases the pressure switch 14.

Each of the contacts 258 extends along a respective lead 262 to acorresponding stationary contact 264 of a read digit pulse emitter 264,266. Wiping contact arm 266 is connected to a direct current source andapplies DC to the emitter terminals 0 to 9 in proper timed relation tothe computer operation. Consequently, when a pulse is applied to theparticular line 262 and contact 258 that is connected to contact arm260, a pulse is emitted at the computer input line 268. Rotary switch264, 266 is part of the computers standard input equipment.

It is possible that the sweep of contact arm 266 for effecting a readoperation might occur during the time that relay 232 is being energized.It will be recalled that the active stroke of the electromagnet 256 doesnot have any direct relation to the stepping switch arms 260, for it isthe spring-return stroke that effects a one-step advance of the contactarms 260. This occurs upon deenergization of electromagnet 256. It mayhappen that the read cycle is initiated just prior to the energizationof relay 232 or it may be that the read interval occurs during the timethat'relay 232 is being energized. If this should occur, then, it isconceivable that the relay 232 and electromagnet 256 might bedeenergized and the contact arm 260 would advance during the readinterval. Conceivably an ambiguous read-out condition couldresult. Toavoid this, the following circuit is provided:

A hold relay 270 is provided, energized by a read hold wiping contactswitch 272 which is part of the computers standard input equipment.Closing of the wiping contact 272 occurs at a time prior to the sweep ofcontact 266 along the active stationary contacts 264 of the read digitpulse emitter, and contacts 272 remain closed until just after contactarm 266 passes the last active contact 264, as illustrated in the readhold portion of FIG. 6.

Energization of relay 270 causes closing of relay contacts 274. Thiscompletes a circuit through isolating diode 276 that bypasses contacts240. Thus, when relay 232 has once been energized by a detected vehicle,and holding contacts 236 are closed during a read interval, it makes nodifference that electromagnet 256 might complete its forward stroke andopen contact 240. If that should occur, the holding circuit for thenegative return of relay 232 would still be complete, extending throughcontacts 236, diode 276, contacts 274, to the negative direct-currentterminal, and both relay 232 and electromagnet 256 would still beenergized. Upon completion of the read time interval, relay 270 isdeenergized and this permits the holding circuit of relay 232 throughcontacts 274 to be opened. Electromagnet 256 presumably has completedits forward stroke and therefore contacts 240 have been opened, breakingthe other possible negative return of the relay holding contacts 236. Itfollows that a vehicle detected during the second read interval is notregistered until after the read interval, when the electromagnet isdeenergized and the contact arm advanced thereby one step.

The normal count frequency that may be expected is of the order ofone-per-second, or slower; and because the read time interval is of theorder of of a second, there will be no loss of a count as a result ofthe holding operation of relay 270.

The counter advances continuously, stepping from one contact 258 to thenext, without reset occurring. The frequency of recycling of thecomputer by internal programming means to inspect the counter in FIG. 7may be anything found desirable. For example, this may occur once everytwo seconds. The internal program of the computer will then compare thecount registered by the digital pulse emitted at line 268 with theprevious count stored in the computer corresponding to this particularcounter. If the new count is higher than the previous one, then thenumber of vehicles detected in that particular interval is simply thedifference between the two counts, and this difference is stored.However, if the previous registered count were higher than the newcount, then presumably the new count is the digit represented by theimpulse transmitted by lead 268, plus 10. The previous count issubstracted from this adjusted value, and this gives the number ofactuations of the vehicle detector during the computer recycling timeinterval. The full cycle capacity of 10 steps in the illustrated counter258-260 is sufficient for practical purposes, it being only requiredthat the interval between each computer evaluation of the counter andthe next one shall be short enough to'k'eep the count difference at avalue of'9 or less, this being the differential count capacity of thecontinuous stepping switch counter 258, 260. Thiscomparing and .countadjusting procedure is carried out through programming of the computer.

The digital clock Calendar data concerning the month, day-of-the-month,the day-of-the-week and holiday indication is all pertinent informationuseful to the computer in automatic selection of an appropriatetraffic-signal sequencing plan or succession of different plans that maybe used during a given day. Such information may be represented bydigits, manually set up on the computer p-lugboard or by means ofselector switches. The digital clock 36 that appears in FIG. 1 performsa number of functions including that of providing time-of-dayinformation used by the computer in calling into operation varioustraffic-signal sequencing plans appropriate to different times of theday. The digital clock serves also in the precise measurement of theelapsed time during each phase of each traffic-signal sequence. Finally,the clock can act as a common time reference for synchronous or properlystaggered operation of all the traffic-signal controllers in the systemwhen controlled by the computer. The wiring diagram of an illustrativedigital clockeifective for the purpose of the described trafiic-signalcontrol system appears in FIG. 8.

The time as measured by the digital clock is an accumulation of seconds,registered in a decimal system so that the clock can reach a count of99,999 seconds (for example) by employing a five-stage counter with tencounts per stage. This takes care of a 24-hour period, which is 86,400seconds.

In FIG. 8 only two stages are illustrated, the units and the tens stage.These include respective ten-position stepping switches 280 and 282. Thetime in seconds is entered into the computer in the manner discussed inconnection with FIG. 7. Each of the ten terminals of stepping switch 280is connected to a respective contact of a read digit pulse emitter,which may be the same one illustrated in FIG. 7. The position of themoving contact 280a determines at what time in the cycle of the digitpulse emitter a pulse will be transmitted from stepping switch 280 ofthe units stage along wire 284 to the computer storage entry. Similarly,an impulse is delivered to wire 286 by stepping switch 282 of the tensstage at a time in the rea cycle which depends upon the position of itswiping contact 282a, thus representing the tens-of-seconds count in thatstage. Three more orders of decimal stages (not shown) build up asecondcounter capacity of 99,999 seconds. Time of day is specified incomputer storage in terms of total number of seconds elapsed pastmidnight, for example. At midnight the clock may be reset to zero or atsome other convenient time it may be set to the appropriate reading inseconds.

The operation of stepping switch 280 is quite similar to the operationof stepping switch 258460 in FIG. 7. Contact arm 280a is coupled by aratchet-andapawl stepping mechanism 287 to the armature of electromagnet288. The contact arm is advanced one step for each cycle of energizationand deenergization of electromagnet 288. An energizing impulse issupplied once eachsecond in a circuit that includes alternating currentsupply line 290, bridge rectifier 292, line 294, operation selectorswitch 296, relay contacts 298, and the opposite line 300 of thealternating current supply. Electromagnet 288 gets D.-C. pulses from thebridge rectifier. Relay contacts 298 are closed once each second byrelay 302 having a suitable source of impulses 304 for deliveringprecisely one impulse per second.

At times the computer may call for a readout operation at a momentbefore the counter is to be indexed or while it is in the process ofbeing indexed. To avoid possible ambiguity in the input to the computer,the same hold timing contacts 272 are used here that appear in FIG. 7,as well as a relay 271 which contacts 275. Contacts 272 close andenergize relay 271 shortly before the read timed pulses are impressed onthe stationary contacts of stepping switch 280 and relay 271 is main:tained energized until after a complete read cycle has taken place.Energization of relay 271 closes relay contacts 275. Stepping switchelectromagnet 288 includes a pair of normally open contacts 306 that arein series with contacts 275 and with rectifiers 308. Contacts 306 closeshortly after the start of the energized forward stroke of electromagnet288. Consequently, once operation of electromagnet 288 has commencedduring a read interval by virtue of the closing of contacts 298, theelectromagnet 288 is maintained energized during that read interval. Theholding circuit for this read cycle includes alternating current line300, relay contacts 275, contacts 306 actuated by electromagnet 288, anda pair of rectifiers 308 which parallel two of the bridge rectifiers andenergize electromagnet 288. At the end of a read interval ofapproximately /5 of a second, contacts 275 open, and unless contacts 298are still closed at that time (as would occur if relay 302 is operatedlate in the read cycle) electromagnet 288 becomes deenergized, andcontact arm 280a is advanced one step Stepping switch 282 of the tensorder of the seconds counter operates exactly in the same manner as thecircuit described in connection with stepping switch 280 with one slightexception. Electromagnet 309 of stepping switch 282 is to receive onlyone advance impulse for each ten impulses supplied to electromagnet 288.For this purpose, cam 310a is mechanically ganged to moving contact arm280a of the units stage and closes cam contacts 310 once in eachcomplete rotation, when contact arm 280a reaches the 9 position. Whenthis occurs, an energizing circuit is established for electromagnet 309,as follows: Starting with alternating current line 300, the circuitextends through relay contacts 298 and selector switch 296, cam contacts310, operation selector switch 312, line 314 extending to bridgerectifier 316, thence along line 318 to the opposite alternating currentsupply line 290. When stepping switch arm 280a is in the 9 position andthe next impulse closes contacts 298, electromagnet 288 is energized foradvancing stepping switch 280 to the zero position. At the same time,electromagnet 309 is energized for advancing stepping switch 282 onestep.

The tens order has a cam 320a and a cam switch 320 which is effective totransmit an impulse to the actuating electromagnet of the next higherorder stepping switch once each time that moving contact arm 282a is inits 9 position. This carry arrangement extends from each order, viamanual selector switch section 322 and others ganged with it, to thenext higher order, up to the highest stage.

By virtue of contacts 324 of the tens stage (comparable to contacts 306already described) and rectifiers 325 and line 326, the position ofcontact arm 282a is prevented from change during a read time interval.By means of this circuit, electromagnet 309 is energized when it shouldreceive an advancing impulse; but actual advance of con tact arm 282a byits spring, ratchet and pawl mechanism 311 cannot occur during the readoperation of the computer.

The digital clock which counts seconds is capable of runningcontinuously with manual selector switches 296, 312 and 322 set asillustrated. Provision is also made to stop the clock, simply by movingthese selector switches one step clockwise, thereby breaking theoperating circuits. It is also possible to test the circuit in a testposition of the manual selector switches 296 and 312, and a resetposition is also provided.

For test and reset operations, a second selector deck 330 is ganged tounits-order l0-position switch 280, and a like 10-position selectorswitch 332 is ganged to selector switch 282. A manual switch 323 isganged to switches 296 and 312. A further ten-position manual switch 336is included in the units stage, and a corresponding switch 337 isprovided in the tens stage of this seconds counter or digital clock. Themoving selector member 336a is conductive and interconnects nine of itsten stationary contacts, only one stationary contact 336a being out ofcontact with selector 336a at any one time, by virtue of its cut-out336b. Selector member 336a can be adjusted to any desired selection from0 to 9.

With the switches of the units order in FIG. 8 set as shown, except foradjustment of ganged switches 296, 312 and 323 to the lowermost or resetposition, a circuit may be traced as follows: Starting withalternating-current supply line 300, and continuing along line 338, the

circuit extends through selector switch 323 and line 340 to conductiveselector 336a; and this selector connects all line 342 together-4xceptfor contact 336c at cut-out 336b -to energize the selector contact armof switch 330 in all positions except that corresponding to the positionof cut-out 3361;; and the circuit continues along line 344 and throughnormally closed contacts 346 of the steppingswitch electromagnet 288,thence via rectifiers 292 to the opposite alternating-current line.

Completion of the above circuit with energization of electromagnet 288by rectifier 292 causes an energized stroke of the electromagnet. Thisopens contacts 346 and deenergizes the electromagnet so as to produce aspringenergized advancing stroke of switch decks 280 and 330. This cycleis repeated until the selector arm of switch 330 finds the wire 342 thatextends to a stationary contact of switch 336 opposite cut-out 33612. Bymanually setting switch 336 at zero, or any other position, the digitalclock can be set at zero or any other indication.

A neon lamp 348 is connected in series with resistor 350 between line338 and manual select-or switch 336 When switch 323 is in the resetposition, and when the positions of switches 330 and 336 agree, all ofthe lines 342 extending from selector disc 336a are open-circuited atswitch 330. However, a circuit extends from lines 300 and 338, throughresistor 350 and lamp 348, along wire 352 and lead 344 through normallyclosed contacts 346, to rectifier 292 and supply line 290. Consequently,when the stepping switch 280 has reached the position called for bymanual selector switch 336, neon lamp 348 lights.

In the foregoing manner, the units order of the clock can be set toprovide any desired digital input for the computer. The higher-orderstages are constructed likewise and each stage can thus be set manuallyto produce any desired initial time digits for the computer, or thisprovision for resetting can be carried out once daily. Other digitalinput to the computer is similarly provided by like apparatus (notshown) for providing month, dayof-the-month, day-of-the-week and anyother set information for the computer.

When the selector switch 323 is in the reset, stop or in the runposition, neon lamp 348 is generally shortcircuited by a circuitincluding selectors switches 323, 336 and 330, one of the lines 342 andline 352. Only by rotating switch 336 into agreement with the numericalposition corresponding to that of switch 280 can neon lamp light. Thisoccurs through a circuit including lines 300 and 338, resistor 350, neonlamp 348, lines 352 and 344, switch 346, rectifier 292 and supply line290. In this way, the manual switches of all the stages of the clockcorresponding to switch 336 can be manipulated with ganged switch decks298, 312, 323, 322 etc. in the stop or the run position, until the neonlamps light, in order to ascertain the clock reading. In the stopposition as shown, the circuit through switch 296 is broken and so theone-second advance impulses are suppressed. In the test position of theswitches all the neon lamps light, and this provides a test of theirbeing operative.

The computer A typical digital computer suitable for purposes of thepresent invention is that described in a booklet entitled Type 650Magnetic Drum Data-Processing Machine Manual of Operation Form22-6060-1, published by International Business Machines, copyright 1955.A brief discussion of some elemental characteristics and capabilities ofthis machine follows, as an illustrative form of the computer in thesystem of FIG. 1. However, the present invention is not dependent uponthis particular machine nor on its specific internal details, and sincesuch detailed information is Widely known and available, the followingdescription of this machine is deliberately general in content and isprimarily intended to provide an orientation and a basis for certainterminology useful in connection with the tratfic signal control system.

This type 650 IBM data processing machine as shown in FIG. 9 includes amagnetic drum 360 for general storage or memory. The general-storagesurface of the drum is subdivided into a series of equal-width bands362, each band extending around the drum and including fifty wordlocations 354. Assuming a 40-band drum is used, the drum has a generalstorage capacity of 2,000 Words. Each word contains ten digit areas.

Each word location is assigned a four-digit identification code from0000 to 1,999. This code includes a twodigit portion from to 49 or from50 to 99 to locate a word position in any pair of the bands, and thecode includes an initial two-digit portion from 00 to 19 to identify aparticular one of the twenty pairs of bands.

Each ten-digit word can represent any value from minus 9,999,999,999 toZero to plus 9,999,999,999; and the digits can be used separately or ingroups to relate to different quantities or to different codes.

The successive individual bands along the drum are provided with aseries of magnetic read-write heads, for sensing the recorded digits andfor re-recording new digits and thereby erasing the previous ones. Thedrum rotates to carry the successive locally magnetized digit areas pastthese heads at high speed. Suitable control circuits suppress or divertthe signals induced in the heads at all locations except at aparticular, selected word location, as identified by any particularstorage address between 0000 and 1,999. These address codes identify aparticular band and a particular one of the 50 areas within the selectedband.

Information for entry into this general storage is supplied from variousexternal information sources or internal sources, in various ways. It issupplied from external sources such as punch-cards or magnetic tapestorage apparatus; and it also originates externally in the presenttraffic-signal control system at the monitor, the counters, and thedigital clock. The externally derived information is not recordeddirectly into the general storage, but instead it is first recorded in aportion 368 of the drum called read buffer storage. Each time the readbuffer storage is to receive new information, it is first cleared, itsentries being transferred to the general storage. The input channels forentry of information can handle 100 digits during a single read cycle.These input digits are divided into ten words of ten digits each; andten words of ten digits each are transferred into general storage eachtime the read buffer storage is cleared.

Information delivered from the machine is also handled indirectly, beingfirst recorded in a portion of the drum 370 called the punch bufferstorage; and from this, it is delivered to the external utilizationapparatus. This output apparatus, like the read portion alreadydescribed, has the capacity to handle 100 digits concurrently.

Much of the matter recorded on the general storage is not information inthe sense of numerical data, but it is in the nature of instructions. Astored instruction includes ten digits and a sign. The first two digitsare an operation code. This may represent add" or multiply or any one ofmany other functions or combinations of functions, the Type 650 IBMmachine having the capacity to execute approximately 90 such functions.The next four digits of this instruction word represent the dataaddress, or the drum location to be selected for use in the particularoperation, or the location in which information is to be stored by theoperation, or other locations, or shifts of digits in the accumulator.The last four of the ten digits represent the address or location wherethe instruction word is to be found for the ensuing operation, whichtakes place after completion of any given operation. The sequence ofinstructions is called a program, and causes automatic operation of thecomputer to utilize stored data and externally supplied information,usually by punch-card read-in apparatus.

The data address and the instruction address for the next operationrelate to the drum if the code is between 0000 and 1,999. In addition tothe storage drum 360, the machine includes a 20-digit accumulator 372,divided into a 10-digit Upper accumulator and a 10-digit Loweraccumulator plus sign; and it includes a Distributor 374. The structionaddress may be 8001 if the distributor is to be the source of the datato be used in the ensuing operation; and the instruction address may be8002 or 8003 when the lower accumulator or the upper accumulatorcontains the data to be used in the operation next following any givenoperation in progress.

A on-digit adder 376 is provided for performing all necessarycomputations, including addition, substraction, multiplication anddivision. It uses information from the distributor and one half of theaccumulator; and it includes a carry loop 378.

A program register 380 is included which obtains addresses and operationcodes from the general storage or the distributor or the accumulator,and it transfers such code-s to an operation register 382 and to anaddress register 384, the Arithmetical and logical operations of themachine are performed by the accumulator, the distributor and the adder.These operations are controlled by the program, operation and addressregisters. Validity checking units 386 are provided at the output of theprogram register, the distriblutor and the accumulator.

The arrangement is such that as each operation is being performed, thenext instruction is being located. Magnetic tape unit-s (not shown) maybe connected to the computer to provide rapidly available auxiliarysources of stored information.

General mode of operation of the system Initial setup consists ofstoring in the computer the necessary program instructions, as well astables of parameters and pre-established data pertaining to the system.This information may be kept on decks of punched cards in which case itmust be read into the computers general storage through the puched cardread-in unit, or it may be kept on magnetic tapes in which case thesetapes must be mounted on the tape units connected to the computer. Theprogram consists of sequences of instructions in the computers codelanguage, including those required to effect the computation of theformulas referred to hereinafter. The tables of parameters andpre-established data may include such information for each intersectionas: the detectors associated with that intersection, their distancesfrom the intersection, the digit positions of input where the input datafor the intersection will appear, the digit positions of output wherethe output data for the intersection must 'be sored, the normal localcontrol se quence for the intersection, data relating to expectedvolumes of turning movements at the intersection, predetermined maximumand minimum limits for traffic signal phase durations, values of fixedphase times (e.-g. amber times), test criteria for changing controlformulas, and any other such information as may be required by theformulas used to determine the computer controlled sequence of thetralfic signals.

In operation with the signals under computer control a repetitive cycleof operations is performed under the direction of the computer program.We shall refer to this cycle as the computation cycle. It begins with aread operation which causes the current values of all the counters andmonitor units in the system as well as the clock information to be readsimultaneously into a designated set of storage locations within thecomputers general storage. This is accomplished by suitable wiring ofthe computers control panel to the external units.

Let us consider the si'gnallized street intersections in the system asbeing numbered from 1 to N. The order of numbering is immaterial. Thecomputer then takes the in put information and the initially stored datapertaining to intersection No.1 and by means of an appropriate formulaor algorithm which would be determined by the engineer or theprogrammer, ascertains Whether any change in the indication of thesignals at intersection No. l is called for at this particular time.This might, for example, be done by comparing the elapsed time since thebeginning of the current phase of the signal, such time beingascertained by a comparison of the current clock reading with thatrecorded at the last detected phase change of the signal, with a desiredor limiting phase duration obtained from a stored table or calculated bya formula referred to above. If the elasped time were found to equal orexceed the desired or limiting time so desired, a phase change would becalled for; otherwise no change would be called for. Depending on theresults of this calculation, the computer stores in a particular outputarea of storage an appropriate code to effect the required change or nochange. No actual output, however, takes place at this time.

The program then proceeds to intersection No. 2 and, using the inputinformation and initially stored data pertaining to intersection No. 2and applying again an appropriate formula or algorithm, which is notnecessarily the same as that used for intersection N0. 1, ascertainswhether any change of signal indication is called for at this time forintersection No. 2, and again stores the apropriate output code. Thisprocedure is gone through for each of the N intersections in turn.Because the computer performs arithmetic operations very quickly thesecalculations can be accomplished for the whole set of intersectionswithin a short interval, for example a little less than two seconds.

When the Nth or last intersection has been processed in this way, anoutput order is given by the computer program which causes all theoutput codes which have been stored during the processing to beconverted to sequences of timed impulses which are sent to the outputunits described elsewhere in the application, thus causing each traflicsignal to maintain its current indication or to change to a subsequentindication. This represents the end of the control cycle and the cycleimmediately repeats with another read instruction. This control cyclemay take a total of approximately two seconds and will continue torepeat in this way so long as the computer is in control of the signals.

In initially assuming control of the system and in finally relinquishingcontrol of the system, an essentially similar sequence of cycles is gonethrough, except that the formulas used for these phases of the operationare designed to ascertain for each signal the proper time to bring itunder or to release it from control of the computer. Output codes areprovided to effect this pickup and dropout, as described elsewhere inthe application. At a given time, any part of the system might be undercomputer control with the remainder operating in its normal locallycontrolled mode. Pickup and dropout programs are designed to effect asmooth transition between these two states.

The formulas used for computing the proper traffic signal change timesmay be as simple, or as complex and sophisticated, as desired, withinthe limits imposed by the speed of the computer. That is, all of theintersections must be processed within the time allowed for onecomputation cycle.

A simple program, in computing the change time for a given intersection,may for example use as data for that intersection only the particularvalues associated directly with that intersection, that is the valuesfrom the counters which are associated with the detectors on theapproaches to that one intersection, the monitor value for thatintersection, the clock data, and the initially stored data for thatintersection. Even with this restriction, there can be considerablevariation in the degree of complexity of the formula used. For example,the formula could take into consideration the density of the traffic onthe different approaches, the number of cars waiting on the red light,and even the speed of traffic if this information were available fromspecialized detectors or could be deduced in some way from theinformation available. Another factor that could be used in the formulais the time of day, day of week, etc., which information is availablefrom the clock input.

Now it will be seen that there is no reason for the information used inthe formula for determining the changes for a given intersection to berestricted to the data from the detectors and controller at thatintersection only. The formula might well utilize information fromdetectors and controllers 1, 2, 3 or more blocks away in any direction.In this way coordination of various degrees may be achieved. In fact,information from any part of the system may in principle be used indetermining the control changes for any given intersection since all ofthis information is simultaneously available to the program. Thecomplexity of the formulas used is limited only by the capacity of themachine to do the requisite calculations in the time available and bythe ingenuity of the engineers and programmers. The amount of storageavailable within the computer might also be considered to be alimitation, but this restriction is largely obviated by the availabilityof magnetic tapes which provide a large amount of auxiliary storagewhich is rapidly accessible to the computer. Thus, at any time duringthe calculations, as a result of criteria built into the program it iscurrently using, the program can automatically make a decision to callin a new set of formulas from the magnetic tapes, and proceed with thesenew formulas. For example, certain criteria might indicate an emergencysituation, such as blockage of a particular intersection, in which casethe computer could call into action a special program which wouldfacilitate rerouting of trafiic around the blocked area. It is quiteconceivable that the machine could be programmed to improve its ownformulas on the basis of experience. This is similar to the idea ofmachine learning which has been investigated with computers in otherfields.

With the advent of computers with higher and higher speeds, thisinvention gives the traffic engineer a tool which he may not yet be ableto fully exploit due to lack of sufficient understanding of the ways oftrafiic. In this connection it may be noted that one of the merits ofthis system is that a complete log of all data recorded, as well as alloperations performed can be kept on magnetic tape and analysis of thisdata may provide the basis for further improved methods of control.

When the data processing machine described is con nected in the systemof FIG. 1, it is prepared for operation by initially entering theprogram instructions, and by entry of information to be stored in theform of tables. These tables contain numbers describing physicalcharacteristics of the system as well as traffic characteristics basedupon the experience, calculations and surveys of traffic engineers. Inpreparing for the entries, a number of desirable plans of traffic signalcoordination are worked out, without being limited to one, two or threesets of schedules. Punch cards may be used for entering the initialinformation and program of instructions, or magnetic tape read-inapparatus or both may be used.

In the operation of the computer for control of traffic signals, the-digit read-in channels usually connected to the punch-card reader areinstead connected to the above-described traffic-signal read-inapparatus, including the digital clock and the monitors and thesteppingswitch continuous counters actuated by vehicle detectors (FIG.1). The output channels from the computer that would ordinarily go to acard-punch unit are here connected to the respective output units (FIGS.1 and 5).

The monitor of each traffic signal in the computercontrolled systemprovides a single digit that represents its phase, such as east-westgreen and north-south red. One read-in digit serves for the phase of asingle traffic signal. One digit also represents the position of eachstepping-switch continuouscounter (FIG. 7) so that, if there are fourvehicle detectors 14 related to a particular intersection, four digits'will convey to the computer the vehicle-count information pertaining tothe related intersection. For example, the first four digits of aten-digit Word in the read buffer may represent the respective positionsof the North, South, East and West steppingswitch counters related to aparticular traffic signal, and a fifth digit may represent the phase ofthat traffic signal,

-e.g., 4096700000. The zeros in this word indicate that there is acapacity for receiving five more digits of like shown in this examplesince the location of each digit of input information is identified bystored tables within the computer.

A word of read-in information comprising ten digits is sufficient forthe digital clock and associated calendar information provided bypanelboard connections or switches (not shown). The first two digits mayrepresent the month, the next two the day of the month, the fifth mayrepresent the day of the week, and the next five digits may representthe time of day in seconds. Using this form, the number 1026451466, forexample, represents October 26, Wednesday, 51466 seconds past mindnight.

The computer may be programmed to have a read-in cycle every twoseconds, each lasting about /s second. The time between read cycles isavailable for data processing. The buffer storage is emptied bytransferring its information to general storage during the first part ofeach read interval, and then the new information is registered in theread buffer. The above representation of a particular traffic signal andits counters, 4096700000, may be routed into the read buffer, and thenby proper instructions in the computer program to general storagelocation 1951. At the same time, the above time-and-date IO-digit word1026451466 may similarly be routed by computer programming to generalstorage address 1960. Concurrently, at these two-second read intervals,cor responding information concerning a second traific sig-. nal and itscounters (represented by the second five digits of the above word) wouldbe routed to the same location 1951 of general storage. The S-digitrepresentations of two more traffic signals and their counters may berouted to general storage location 1952. In this way, the five-digitrepresentations of 18 traffic signals and their counters can beregistered concurrently in general storage locations 1951, 1952 .1959.Location 1960 may be reserved for the time-and-date IO-digit code word.

In a sequence of nine two-second computation cycles, considering onlyone trafic signal and a -digit timeand-date word, the digits inlocations 1951 and 1960 may be:

Cycle Location 1951 Location 1960 etc etc. etc.

Numbering the digit positions in the above codes from 1 to 10, startingat the left, the digits refer to the following:

Location 1951, Digit 1-North Counter Location 1952, Digit 2South CounterLocation 1951, Digit 3--East Counter Location 1951,.Digit 4West CounterLocation 1951, Digit 5-Monitor Location 1960, Digits 1 and 2Month(October) Location 1960, Digits 3 and 4Day of Month (26th) Location1960, Digit 5-Day of Week (Wednesday) Location 1960, Digits 6 to 10,incl-Time of Day in Seconds The following information may be deducedfrom the tabulation (above) of 10 read cycles:

(a) Total elapsed time-18 seconds (b) Total north counts received- 7 (c)Total south counts received-7 (d) Total east counts received6 (e) TotalWest counts received2 (f) The traffic signals changed from East-Westgreen through a 4-second East-West amber phase into the North-Southgreen phase.

Between each /5-second read-in operation and the next, the machineperforms logical and computing operations utilizing the information fromeach digit of the digital clock and of each trafiic-signal group of fivedigits, as well as information from pre-recorded tables. During the timebetween each /s-second read-in operation and the next, two seconds laterin this example, the computer programming causes successive computationsto be made relative to one traflic signal after another. If there are 18differ.- ently controlled trafiic signals, then the computer performs 18complete sequences of computations in suc-. cession within the timebetween each read operation and the next. At the end of the computationinterval, concurrent read-out operation to all the controlled signalsoccurs, each with its own control channel.

As a measure of traffic density during a particular phase of a trafficsignal, the computer may be programmed to ascertain the maximum numberof vehicles detected in any 10-second interval. By suitably programmingthe computer, the information in location 1951 may be transferred tolocation 1971; and in the next 2-second interval the information inlocation 1951 may be routed to location 1972, and in four more cyclesthe information in location 1951 may be transferred to locations 1973,1974, 1975 and 1976. The programmed computer subtracts the stored, fixeddigits in location 1971 representing the initial state of the countersfrom the value in location 1976 and records the difference in anothercoded location, e.g. 1981. In this example, if the initial counterreadings are 4096700000 in location 1971 and if the counters step alongprogressively to reach 7327800000 ten seconds later, the first counterhas advanced from 4 to 7, and so has advanced 3 counts. This value canbe registered in location 1981. The second counter, having advanced from0 to 3 will have detected 3 counts and the second counter-representingdigit recorded in location 1981 as a result of the programmed computeroperation will also be 3. The third counter has advanced from 9 to 2;and since the computer recognizes 2 as less than 9 it adds 10 to 2 andsubstracts the 9 from 12, giving 3 counts for the third counter. Thefourth counter has advanced only one. The first four digits stored inlocation 1981 on the basis of the above computations are 3331,representing the actual number of vehicles that were detectedapproaching a certain intersection from four directions during the10-second interval, assuming placement of four vehicle detectors 14(FIG. 1) to detect vehicles along these approaches.

At the seventh read-in cycle following the above phase change, the newcount reading can be transferred from location 1951 to location 1971,erasing the first one in location 1971; at the eighth cycle the newinformation can be transferred to location 1972; and so on. During eachcomputation cycle that follows each read-in operation, the computersubtracts the earliest stored number from the latest, and therebyobtains the l-second traflic rate. If it exceeds the value previouslyregistered in location 1981 (as determined by a programmed comparison)the new, higher value can then be registered there.

During times when traffic is light, it may well be advisable to leavecontrol of the local traffic signals to their local sequencingcontrollers, according to a useful application of the disclosed system.When a rush-hour arrives, at a preset time stored in the computerprogram and checked against the digital clock automatically, thecomputer then assumes control of some parts or all of the supervisedsignal control system. This is achieved by sending a hold impulse viathe circuit of FIG. to that of FIG. 3.

Traflic-responsive control of individual trafiic signals has beendiscussed, in which it appears that only one digit is involved in phaserepresentation while four more digits are involved (in an example) inregistering counts of vehicle detectors. Traflic density may not be ofparticular interest in a system where accurate traffic flow can bepredicted with reasonable accuracy. In that event, a number of timecycles can be recorded as parts of a plan stored in the computer, eachsignal to be monitored and controlled by only one read-in and oneread-out digit. A system of 90 differently controlled traflic signalscould then be accommodated in this manner by the illustrative computer,changes from one plan to another being dictated by read-out from thedigital clock as compared with stored clock readings at which each planis to be called into effect. Also, detectors at key locations may beused to contribute to plan selection for a large system of trafficsignals.

The capacity of the general storage of drum 360 in the illustrativecomputer is limited, and may not be enough to accommodate the number ofdifferent plans required by the central trafiic control system. In thatevent, additional plans and program instruction may be made available tothe computer in the form of quick-access magnetic tape storage units.Manually in advance or automatically at programmed times of day, whichmay differ depending on the day of the week and on certain dates of theyear, the computer may cause substitution in its general storage ormemory of a program available inan auxiliary tape storage unit in placeof that currently in its general storage. In this way a large number ofdifferent plans of traffic signal coordination that have been founddesirable at different times may be brought into effect as desired.

Each plan may be modified at the central location, without tediouson-the-scene adjustment of each individual traffic-signal controller, asis required with usual locally controlled units. The total elapsed timeof the complete sequence of phases in each control cycle can readily bechanged, making it long or short as may be desired. Multiple signals maybe coordinated, for example staggered or offset in a predeterminedrelationship, and the direction and speed of traflic flow favored bystaggered signals may be changed at different times, automatically or atwill, using readily available previously prepared signal control plansand computer programs.

The adaptation of trafiic signals to digital control by means of acentral digital data processing machine is seen to be of great advantagefrom many points of view. Large numbers of control plans fortrafic-signal systems can be quickly and automatically put into effecton the basis of predicted times, traffic density, or other criteria.Changes in any plan can be made with comparative ease, at a centrallocation and without resort to mechanical changes for large numbers ofindividual sequence-timing units. The vast flexibility and newpossibilities of the system disclosed are of particular importance inrelation to the growth and complexity of signal-controlled trafficnetworks.

A broad range of modification and varied application of the novelfeatures described above will occur to those 28 skilled in the art, andtherefore this invention should be broadly construed in accordance withits full spirit and scope.

What we claim is:

1. Apparatus for remotely evidencing the selective positioning of arotary multi-pole selective switch in a local traffic signal control,comprising a transmitter at a first station location, said transmitterincluding a plurality of rotary coaxial earns, a plurality of switchescooperating with said cams respectively and operable thereby to open andclosed conditions, coordinating means connecting said cams to saidselective switch, said cams having related contours such that eachselective position of said selective switch has a corresponding uniquecombination of open and closed cam-operated switches, signalling meansat a second station location remote from said first station location,said signalling means including a plurality of terminals correspondingto the predetermined positions of said cams, energizing means, aplurality of switching relays equal in number to the number of saidcam-operated switches and having energizing circuits connecting thecoils of said switching relays to respective ones of said cam-operatedswitches, a plurality of display-actuating relays equal to the number ofpredetermined positions of said cams, means connecting said switchingrelays and said display-actuating relays to said energizing means, eachof said display-actuating relays including first and second contactpairs, a plurality of phase-representing lamps connected to said contactpairs for displaying the phases of a traffic signal in response to theswitching of said display-actuating relays, including means connectingsaid lamps to said energizing means, each of said switching relayshaving first and second sets of double-throw contacts, the contacts ofsaid first set being connected in cascade to said plurality ofterminals, the contacts of said second set being connected in cascade tothe coils of said displayactuating relays, said terminals being adaptedfor connection to a digital read pulse emitter of a digital computer,said first contact pairs of said display-actuating relays and saidsecond contact pairs of a group of said display-actuating relays beingednnected to said lamps and to said energizing means for selectivelyenergizing the connected lamp, and a flasher switch, said second contactpairs of another group of said display-actuating relays being connectedin a circuit to said energizing means, said flasher switch beinginterposed in said circuit in control thereof.

2. Apparatus for remotely evidencing the phase of a local trafficsignal, including signal display control means proximate to said signalfor establishing said phase, and further including a remote monitoringsystem including a plurality of display relays equal to the number ofthe traffic signal to be represented, energizing means, switching meansfor energizing said display relays selectively in accordance with theselected phase of the local traffic signal, including means connectingsaid switching means to the coils of said display relays, meansconnecting said display relays and said switching means to saidenergizing means, each of said display relays having first and secondcontact pairs, a plurality of indicator lamps, means connecting each ofsaid first contact pairs and each of said second contact pairs of afirst group of said relays in series with a predetermined lamp and saidenergizing means, a flasher switch, and means connecting said secondcontact pairs of a second group of said relays in series with saidflasher switch, said energizing means and predetermined ones of saidlamps.

3. Apparatus in accordance with claim 2, including third contact pairsfor predetermined ones of said display relays of said second group, saidthird contact pairs being connected to predetermined ones of said lampsand to said energizing means.

(References on following page)

2. APPARATUS FOR REMOTELY EVIDENCING THE PHASE OF A LOCAL TRAFFICSIGNAL, INCLUDING SIGNAL DISPLAY CONTROL MEANS PROXIMATE TO SAID SIGNALFOR ESTABLISHING SAID PHASE, AND FURTHER INCLUDING A REMOTE MONITORINGSYSTEM INCLUDING A PLURALITY OF DISPLAY RELAYS EQUAL TO THE NUMBER OFTHE TRAFFIC SIGNAL TO BE REPRESENTED, ENERGIZING MEANS , SWITCHING MEANSFOR ENERGIZING SAID DISPLAY RELAYS SELECTIVELY IN ACCORDANCE WITH THESELECTED PHASE OF THE LOCAL TRAFFIC SIGNAL, INCLUDING MEANS CONNECTINGSAID SWITCHING MEANS TO THE COILS OF SAID DISPLAY RELAYS, MEANSCONNECTING SAID DISPLAY RELAYS AND SAID SWITCHING MEANS TO SAIDENERGIZING MEANS, EACH OF SAID DISPLAY RELAYS HAVING FIRST AND SECONDCONTACT PAIRS, A PLURALITY OF INDICATOR LAMPS, MEANS CONNECTING EACH OFSAID FIRST CONTACT PAIRS AND EACH OF SAID SECOND CONTACT PAIRS OF AFIRST GROUP OF SAID RELAYS IN SERIES WITH A PREDETERMINED LAMP AND SAIDENERGIZING MEANS, A FLASHER SWITCH, AND MEANS CONNECTING SAID SECONDCONTACH PAIRS OF A SECOND GROUP OF SAID RELAYS IN SERIES WITH SAIDFLASHER SWITCH, SAID ENERGIZING MEANS AND PREDETERMINED ONES OF SAIDLAMPS.